Rock drill bit and method of manufacture thereof



Feb. 28, 1961 J. s. EDGAR ETAL 2,973,047

ROCK DRILL BIT AND METHOD oF MANUFACTURE THEREOF Filed Nov. 6. 1958nI/EJ-ZZLC/FE dof/Al SEDGAR dof/Al K/NG Unid ROCK DRILL BIT AND METHODOF MANUFACTURE THEREOF `"numstanley Edgar and John A.vKing,si.tzmharines,

"Ontario, Canada, assignors` to Thompson' Products,

Ltd., St. Catharines, Ontario, Canada, a corporation of Ontario The.Ypresent 'invention relates broadly r-to rockegdrilling, and; ismoreparticularly; concerned with` anovel article tand new `and improved`method of producing Athe-same featuring an'` essentially continuousalloy coating covering the drill bit body, functioning to securetheinserts there- :.in, reduce stress concentrations in notches uin thebody surfaces and to eliminate the need for shims between :.thebody anddrill rod.

Although the teachings of the present invention will :bei-applicable toanumber of phases in the drilling art, the particular invention will bedescribed in ,detail in connection with rock drill bits. Such bitscomprise a metal drill bit body, usually made of steel, having carbide:inserts mounted on the drilling face thereof and having a :socket onthe back thereof for receiving the shank. It is vconventional practicein the art to assemble the bit `bodyv and inserts by first heating thecomponents to vbnazingtemperature, and after applying a suitable flux,obtain securement between the components by use of brazing material in apreformed shape or by use of a brazing rod which is melted into thejoint areas in Sullicient quantity to fill the joint. It has been found,however, that a common problem associated with carbide bit bodies isfatigue failure during use. Whilethe causes of such fatigue may be many,generally, it is believed that the fatiguearises from machining, forgingand like notches in the surface of the ,steel bit body which concentratestresses and result in progressive cracking, eventually weakening theparticular `area until brittle fracture occurs.

"In addition, one manner of effecting a friction fit be- `tween thedrill bit and drill rod is to employ a shim of relatively softermaterial between the tapered end of the drill rod and the mating taperedsocket in the drill bit. j The shim material is generally copper, brassor bronze, -and since it is softer than the mating parts, the shimswages in use and accommodates imperfection in fit between the taperedareas of the drill rod and drill bit socket, to provide a betterconnection. The shim, by keeping the two steel surfaces separated,reduces the `tendency toward fretting corrosion and galling, which alsocause fatigue failure. The shim is, however, not an integral part ofeither component of the connection, and as will be noted shortlyhereinafter, the present invention obviates the need for this separateshim.

,-.It is therefore an important aim of the present inven- Ation toyprovide a rock drill bit #and method of producing the, same whichavoids each of the objects and disadvantages of the prior art structuresand methods.

. Another object of this invention lies in the provision -of a method ofmanufacturing drill bits having carbide orsimilar inserts mounted on thedrilling face thereof, Y. said-.method providing a bit having surfacesessentially free of exposed machining and forging marks and thereby tfeaturing a substantial reduction in the stress concentra- ...tions in saidrbit.

.Q Still another object of the present invention is to prol atent1k-v'icle a rock'd'rill bit carrying upon the surfaces thereofl ec2,973,047 Patented Feb. 28, 1961 -ai-.lmfnor coatingofr'fiallcysmaterial effective towrigidly Asecure the carbide insertstoVthegdrillbit,bodyI and addivtionally ,to achieve noticeable increasesgin; thefatigue resistance properties of wthe bit` body.

A further object;ofthefinvention-,liesin.the provision of a method ofproducing-insert inountingdrill bit-assemr`blies;'featuring coatingfthe.exposed surfaces Of'thesinserts and drill bit bodywithfacontinuousiiilmofbrazng material, the coating procedure.functipninsinadditien to .provide` a ,heatingV cycle Ifor:V halfllillgvthev steel compo- ;nents of the bit; body.

;An even furtherobject of '-the3inventionpis toprovide a drill bit 1assembly-wherein the vtrod.; socket walls; are 'Coated Withvy2111:2.1110511filmintegral therewith. to'V thereby -obviate ,theuse-of-az separa,te;;.Shim-V4 between the rods and socket.walls.

, A 'stilli further ,y object' :of-this qinyention' isi to provide f aY, method of g fxedly securing lcarbide e ninserts -within notches inadrillfbit body@whichgm-ay bel performed by a minimums numbergof'-personnel,- ,results in substantial production economies,lande-.provides afinalv article of substantially improved properties f,and', characteristics.

Otherobjects and advantages :will becomernore appar- -entduring thecourse, of the-following description, particularly when-taken inconnectionrwith the accompanyying drawings.

. In the drawings,v wherein like; numerals are employed ..todesignatelike partsthroughout the-same:

i Figure lis a vfull'yiewgin `elevation of a drill bit assemblyembodyingthe principles ofgthel present invention;

AvFigure 2 is gan elevational; sectional view takenV substantially alongthe line II- 1I of-Figure 1; and

; Figure 3 `is ay vertical sectional viewftaken substantially ,.-alongthe-line III-III of Figure 2.

Referringsnow'tothe-drawings, in Figures- 1 and2 there vis-'shownaydrill; bit assembly indicated generally by the reference g numeral 10,which; comprisesametal drill bit body' 11- having a wall portion-11adefiningtt V'generally cylindrical (but tapering l slightly inwardly)shank-receiving socket therein, andv a metal shank or rod 112 adapted tobe press-fit into the socket; denedby;the

walls 11a and having a corresponding wall portionv 12a for. engaging thesocket wall .portion 111:1. Inaccordance -With-the principles ofthisfinvention, thegmetalidrill bitbody -11 is provided upon itsvexposed surfaces -with -a relatively-thin metallic alloy coating orfilm 13 effectively improving the fatigue resistance ofthe lbit body,and yas `will be described in detail later, rigidly.4 securingfthe isgrooved-at 16a, 16b, 16e and 16d on the drilling .face

11b between the inserts 15a, 15b, 15e and 15d. Accordingly, the drillingfluid path is downwardly through the central aperture 4, thennadiallyoutwardly through channels v'at 17 on the drilling .face 11b,andthenlongitudinally back or upwardly'through channels designated as18. Anaxially aligned channel 19 is proyiydedhinA the shank or rod 12forthe' flow Yof drilling fluid downwardly throughout the entire length`of the' shank 12 into the drill bit socket defined by i t he walls 11aand on downwardly through theaxiallyr yalignedA aperture 414-in the bitbody 11. The-shank 12 Yin many-cases'V does not-seatcompletely-in'thesocketyand a space S ifpresent 'therein alsoislled:withV drillinguid. Thef'details-of structure outlined in thepresent paragraph are merely exemplary of the type of drill bit assemblywhich may be used in lthe practice of the present invention; and it willbe appreciated that various other drill bit body structures may also beused, the essence of the present invention residing in the coating 13and its method of application to the drill bit body 11.

The coating or film 13 covering the entire surfaces of Y -inserts 15positioned in the grooves 11e therein, as well as providing a brazedfilm upon the entire' surfaces of the bit body 11 eliminating exposedmachining and forging marks and thereby substantially improving thefatigue resistance of said drill bit body 11. Further, the moltenbrazing material provides the means of heating the steel body to thehardening temperature of the steel, and eliminates the prior artrequirement of separate shims between the shank and socket.

The bit body 11 is formed of alloy steel and the inserts 15 preferablyof straight tungsten carbide with a cobalt binder. Accordingly, theknown silver brazing alloys or silver solders, being ternary alloys ofsilver, copper and zinc in varying proportions, provide a particularlysatisfactory composition for the coating 13. Addition metals such ascadmium, tin, nickel, manganese and phosphorus may of course be used inthe brazing composition. The silver brazing alloys perform particularlywell in the present application by reason of their strength, low meltingpoints, free flowing properties and resistance to corrosion; however,the brass and nickel silver brazing alloys or spelter solders haveproperties and characteristics which render them also suitable in theformation of the coating 13. Depending upon the particular percentagesof silver, copper and zinc in the brazing alloy composition, the meltingpoint generally varies from about 1165 degrees to 1450 degrees F. andthe ow point between about 1200 degrees 'and 1565 degrees F.

Preparatory to application of the brazing alloy to the surfaces of thedrill bit body 11 and inserts 15, the parts are cleaned to removesurface scale or oxides, as well as oil, grease land dirt. This may beaccomplished in the manner customary in the amt. The parts are thenpreferably fluxed, and the borax materials are suitable in dry, paste or`saturated solution form.` Certain of the special uxes may also beemployed, and dipping or brushing practices are satisfactory. Particularconditions may, however, render fluxing unnecessary, without sacriiicein -braze strengths.

In order to elect a proper brazed joint between the inserts 15 and drillbit body -11, it is generally required that clearances existtherebetween. In other words, the generally rectangular ygrooves 11cshould be of sufficient width to easily accommodate the inserts 15, witha small gap between the outer surfaces of the inserts and inner surfacesof the grooves. Accordingly, prior to dipping the bit body with theinserts thereon into the molten brazing alloy bath, relative movementbetween the body and inserts should be prevented. This may beaccomplished in -any desired manner, and a technique which has provenelective in practice is to swedge' a plurality of lips from the steelbody over the edges of the carbide inserts. In large scale production afixture is used to produce a number of lips in 4a single operation, andfor lesser quantities a hammer and punch is used. Other methods may ofcourse be employed, and under particular conditions the use of swedginglips may not be required.

The brazing alloy is preferably melted in a refractory con-tainer andcovered with ux to prevent oxidation. The bath may be heated by any ofthe methods used with pot furnaces, and if desired, the parts to becoated may be preheated to minor extent. The temperature of the alloybath is maintained at about the ow point of the particular alloy beingemployed, and the length of dipping or immersion time will varywith thealloy, the size and composition of therparts being coated, andof coursethe particular thickness of coating desired. Nofrmally, however, arelatively slow single dip stroke will be sufiic-ient for mostapplications.

Upon removal from the bath the bit body 11 and the inserts 15 located inthe grooves 11c therein are found to carry a coating 13 of essentiallyuniform thickness throughout. As is shown in Figure 3, the coating 13effects a uniform thickness brazed joint between the inserts 15 and thewalls of the grooves 11e in the bit body 11. A rigid joint or bond isobtained by surface alloying of the base metal and the brazing metalwhich is of suicient strength to adequately maintain the inserts withinthe .grooves 11c. Further, by the coating of this invention, the entiresurface area of the bit body 11 is essentially free of exposed machiningand forging marks. Therefore, when a force is applied to the drill bit,there is not the usual surface imperfections to cause stressconcentrations. Brittle fracture is accordingly markedly reduced.

In addition, since the wall portion 11a defining the shank receivingsocket carries an adherent iilm of brazing alloy which is an integralpart of the body 11, the prior art requirement of separate shims betweenthe shank or rod and body is eliminated. Thus, as earlier noted, it isno longer required that a relatively thin shim of copper, brass, bronzeor like softer material be employed between the mating surfaces of thedrill rod 12 and drill bit socket wall 11a, in order to effect thefriction iit wedged attachment between the rod and drill bit.

The method of this invention employs commercially available materials,and is accordingly characterized by substantial economies in itspractice. The process may be performed in a minimum length of time withonly .a limited number of personnel. The results to be obtained arereadily predictable, and the product obtained is characterized bysuperior strength and the other advantages earlier noted.

It is to be understood that variations 1and modifications may bepracticed in the methods and articles herein disclosed without departingfrom the novel concepts of the present invention. v

We claim as our invention:

l. A drill bit for rock drilling and the like, comprisin a shank, a bitbody provided with a shank socket receiving said shank, insert receivingnotches in said body and inserts in said notches, and an essentiallycontinuous dip coating of brazing alloy material entirely covering saidbody and bonded to the body shank socket walls and to the notch surfacesand inserts therein tto effectively reduce stress concentrations in saidbody, to bond said inserts to the body and to eliminate the need forseparate shims within the shank socket to hold the shank therein.

2. A drill bit for rock drilling and the like, comprising a Ibit bodyand drilling inserts carried by said body and located in notchesprovided therein, and a layer of alloy material of substantially uniformthickness bonding the inserts to the bit body notch surfaces, the samealloy layer essentially completely covering the -bit body and inserts toeliminate exposed surface imperfections in lthe body and reducesubstantially stress concentrations therein.

3. A drill bit for rock drilling and the like, comprising a bit 'bodyand drilling insert-s carried by said body and located in notchesprovided therein, and a dip coatingof alloy brazing material ofsubstantially uniform thickness bonding the inserts to the bit bodynotch surfaces, the same dip coating essentially completely covering thebit body and inserts to eliminate exposed surface imperfections in thebody and thereby: reduce substantially stress concentrations therein.

4. A method of producing drill bit assemblies for rock drilling and thelike, comprising locating a drill bit body with a plurality of insertsin the notches thereof in submerged relation within a bath of alloymaterial, and coating the body and inserts with an essentiallycontinuous lm of alloy material of substantially uniform thicknessthroughout to bond the inserts to the body while eliminating exposedsurface imperfections in the body and thereby reduce stressconcentrations therein.

5. A method of producing drill bit assemblies for rock drilling and thelike, comprising locating a plurality of inserts within notches in adrill bit body, restraining said 15 inserts against movement relative tothe body, and dipping the body and inserts thereon into a bath ofbrazing alloy material to bond -the inserts to the body and coat saidbody and inserts with a coating of substantially uniform thicknessessentially completely encasing the body and inserts to eliminateexposed surface imperfections and thereby reducing stress concentrationtherein.

References Cited in the le of this patent UNITED STATES PATENTS1,697,086 Pryce Ian. 1, 1929 2,698,810 Stauifer Jan. 4, 1955 2,743,495Eklund May l, 1956 2,875,110 Rossander Feb. 24, 1959

